textproduct: Rapid City

KEY MESSAGES

- Windy, mainly dry and unseasonably warm this week.

- Record to near-record high temperatures on Christmas.

- Chance of snow and much colder, but seasonal, this weekend.

DISCUSSION

(Today Through Monday) Issued at 122 AM MST Tue Dec 23 2025

Latest upper level analysis shows slightly zonal flow over the forecast area with a building ridge over the central CONUS and a deepening trough in the Eastern Pacific extending from a strong upper low off the coast of British Columbia. Water vapor satellite has a well defined Chinook Arch over Colorado that extends northward into eastern Wyoming (off the Laramie Range). At the surface, two east-west frontal boundaries are situated over the area. One boundary extends across northwestern South Dakota, while the second boundary extends through northern Wyoming into southwestern South Dakota and northern Nebraska. Additionally, high pressure is centered over Saskatchewan with ridging extending down to the boundary in northwest South Dakota. Temperatures at 0830Z are mild, mainly in the 30s, with a few readings in the lower 40s in the foothills around Rapid City.

The upper ridge over the Central Plains will build today and shift slightly east as the eastern Pacific trough deepens. This will create a more pronounced southwest flow pattern in the upper levels. The northern surface front will wash out as surface high pressure drops into the eastern Dakotas. This set-up will allow for return flow to develop over the forecast area this afternoon with a modest pressure gradient due to the proximity of the southern frontal boundary. Breezy southeasterly winds will be common east of the Black Hills to the north/east of the boundary, while breezy southwest winds develop on the west/south side of the boundary across portions of northeastern Wyoming. It will be slightly cooler today, especially after the record warmth on Monday, but it will still be unseasonably warm.

Southerly flow and warm air advection tonight combined with 30-35kt winds in the lower levels, will keep temperatures from dropping off across the southern 2/3rds of the area, with some locations in the Hills and Foothills warming overnight.

A weak, moisture starved impulse rounds the ridge Wednesday morning as the southern surface frontal boundary lifts northward. The timing of these two features, combined with the lower sun angle this time of the year, will limit the daytime heating potential by a few degrees. Temperatures will continue to be unseasonably warm, but will likely remain below record highs. Records for selected locations Wednesday include KUNR 67F, KRAP 62F, Gillette 62F, Hot Springs 62F, Camp Crook 52F, and Winner 59F).

Model consensus and certainty has increased over the past 24 hours, with the upper ridge remaining anchored in place over the Central Plains through Friday. Models still indicate weak impulses rounding the ridge Christmas, Christmas night and Friday, but are keeping 850mb temps around +15F. Record highs are a little lower in spots on Christmas than Wednesday, thus there is the potential for record warmth Christmas Day. (Records are: KUNR 63F, KRAP 60F, Gillette 55F, Hot Springs 62F, Camp Crook 52F, and Winner 66F). Additionally, a 40-50kt low level jet will aid in warming. There will also be a chance for some very light rain showers/sprinkles with these impulses.

The upper ridge breaks down after Christmas. The eastern Pacific upper trough swings through the region Saturday and closes off an upper low over Ontario Saturday night. Northerly flow behind the trough will result in much colder, but seasonal, temperatures for the weekend. Precipitation chances will be minimal, with some snow showers possible with the overrunning of cold air. Brisk northwest winds, especially over the South Dakota Plains, may result in sub-zero windchills Saturday night.

AVIATION

(For the 12Z TAFS Through 12Z Wednesday Morning) Issued At 405 AM MST Tue Dec 23 2025

VFR conditions through the period.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.